1. Field of the Invention
The invention relates to an imaging device and in particular, to an imaging device capable of switching between a photographing mode by a first still image photographing part and a photographing mode by a second still image photographing part.
2. Description of Related Art
Camera-shake correction technology of still images is a technology to alleviate blurring of images due to hand movement when still images are taken. This is achieved by an element that detects camera shake and an element that corrects an image based on the detected result.
In a method for detecting camera shake, a method uses a camera shake sensor (angular rate sensor) and a method electronically detects camera shake by an image analysis. As a method for correcting images, there are a optical type camera-shake correction that corrects images by an optical operation and an electronic type camera-shake correction that corrects an image by image processing.
As to a still-image camera shake correction, there are a method that detects camera shake by a sensor and optically corrects the camera shake based on the detected result, a method that detects camera shake by a sensor and electronically corrects the camera shake based on the detected result, and a method that electronically corrects camera shake by image processing.
The method that electronically corrects camera shake based on the camera shake detection result by image analysis is called a full electronic camera shake correction. As a full electronic camera shake correction system that is put to practical use, there is a system in which a plurality of short time exposure images (divided images) G1 to G4, each of which having its exposure time T2 obtained by dividing normal exposure time T1, are aligned and combined according to their image characteristics, thus producing a still image G (an image addition type camera shake correction), as shown in FIG. 1.
In the image addition type camera shake correction, if each divided image fully coincides with each other by an alignment, the amount of camera shake is reduced to an exposure time of one divided image. However, in the image addition type camera shake correction, the period of time from the beginning of exposure for the first short time exposure image G1 to the end of exposure for the last short time exposure image G4 may become longer than a normal exposure, and thus, there is a drawback that the degree of camera shake of the photographic subject during that time period may be larger. Moreover, if the alignment by the image processing fails, the camera shake may become larger than a normal exposure, unfortunately.
Japanese Laid Open No. 9-261526 describes an imaging device that takes pictures serially with an exposure time that does not cause camera shake under a low brightness condition, and combines a group of such underexposed images after correcting mutual misalignment among the plurality of images, to obtain an appropriate image without blurring.
Japanese Laid Open No. 2004-221992 describes an imaging device and program in which the imaging device has a control means that sets up one of a first photographing mode and a second photographing mode depending on the conditions at the time of photographing, such as brightness of the photographic subject, focusing length, aperture, and photographic sensitivity, in which the first photographing mode obtains a combined image that is exposure-adjusted by combining a plurality of images taken in series, and the second photographing mode obtains an image that corresponds to the combined image by one shooting.
One purpose of the invention is to provide an imaging device having a still image photographing mode based on a one-shot exposure and a still image photographing mode based on divided exposures, in which the imaging device makes a prediction before still image photographing is started as to whether an alignment of a plurality of images obtained by the still image photographing mode based on the divided exposures is normally performed, and automatically switches the photographing modes depending on the predicted result.
Another purpose of the invention is to provide an imaging device that makes a prediction of whether an alignment of the remaining images is normally performed during still image photographing based on divided exposures, and automatically determines whether to continue the divided exposures or to perform a one-shot exposure of the remaining part depending on the predicted result.